Following the overpopulation of 2100 and mass starvation that followed, the World Government declared that all males between 12-21 were fair game to become food for the plate of anyone able to catch them.
At first just boymeat restaurants popped up, but soon their were so many boys to be eaten that mass production began. Boy processing factories opened up, producing boy meat for the supermarket shelves.
It replaced beef and chicken as the main food of choice in the west. To fill the quota anyone under 21 who committed a crime, no matter how tiny, was turned into delicious meat, but that wasn't enough so soon the government began encouraging parents to sell off spare children for cash.
Finally, the government began using school to teach children that becoming meat was great. Mass brainwashing some called it, but not many people complained because now their was even more delicious meat that volunteered to be on your plate.

To combat the gender unbalance, some genius scientist invented a drug that when put into the water supply made sure that 80% of children born were male. 60% of boys would end up food before 21, and so population was controlled and the human race prospers to this day.